In a wireless communications network, each device needs to transmit information by using a frequency resource. The frequency resource is also referred to as a spectrum. Spectra may be divided into a licensed spectrum and an unlicensed spectrum. The licensed spectrum is a dedicated frequency resource, and the unlicensed spectrum is a public frequency resource.
As communications technologies develop, increasing information is transmitted in the wireless communications network.
An unlicensed spectrum may be preempted to transmit information, so as to increase a data throughput in the wireless communications network and better satisfy a user requirement.
However, in the prior art, when a device successfully preempts a channel of an unlicensed spectrum, data may be sent at a random time, and consequently, a first subframe that is sent by the device may be an incomplete subframe. Referring to FIG. 1, in this case, a receive end cannot determine a quantity of OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexing) symbols included in an incomplete first subframe, and cannot correctly receive the incomplete subframe.